Liquid Crystal Composition and Liquid Crystal Display Device

ABSTRACT

The subject is to provide a liquid crystal composition that satisfies at least one characteristic among the characteristics such as a high maximum temperature of a nematic phase, a low minimum temperature of a nematic phase, a small viscosity, a large optical anisotropy, a large dielectric anisotropy, a large specific resistance, a high stability to ultraviolet light and a high stability to heat, or that is suitably balanced regarding at least the two characteristics. It is to provide an AM device that has a short response time, a large voltage holding ratio, a large contrast ratio, a long service life and so forth. 
     Means for Solving the Subject 
     The invention provides a nematic liquid crystal composition that include a specific optically active compound as a first component and a specific compound having a positively large dielectric anisotropy as a second component, and that may include a specific compound having a high maximum temperature or a small viscosity as a third component, and a specific compound having a small minimum temperature and a positively large dielectric anisotropy as a fourth component, and provides a liquid crystal display device including this composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates mainly to a liquid crystal composition suitablefor use in an AM (active matrix) device, and an AM device containing thecomposition. More specifically, the invention relates to a liquidcrystal composition having a positive dielectric anisotropy, and adevice having a mode such TN (twisted nematic), OCB (opticallycompensated bend), IPS (in-plane switching) or PSA (Polymer sustainedalignment), and containing the composition.

2. Related Art

In a liquid crystal display device, a classification based on anoperating mode for liquid crystals includes phase change (PC), twistednematic (TN), super twisted nematic (STN), electrically controlledbirefringence (ECB), optically compensated bend (OCB), in-planeswitching (IPS), vertical alignment (VA), and polymer sustainedalignment (PSA). A classification based on a driving mode in the deviceincludes a passive matrix (PM) and an active matrix (AM). The PM isfurther classified into static, multiplex and so forth, and the AM isclassified into a thin film transistor (TFT), a metal-insulator-metal(MIM) and so forth. The TFT is further classified into amorphous siliconand polycrystal silicon. The latter is classified into a hightemperature type and a low temperature type according to the productionprocess. A classification based on a light source includes a reflectiontype utilizing natural light, a transmission type utilizing a backlightand a semi-transmission type utilizing both natural light and abacklight.

These devices contain a liquid crystal composition having suitablecharacteristics. The liquid crystal composition has a nematic phase.General characteristics of the composition should be improved to give anAM device having good general characteristics. Table 1 below summarizesthe relationship between the general characteristics of the two. Thegeneral characteristics of the composition will be further explainedbased on a commercially available AM device. The temperature range of anematic phase relates to the temperature range in which the device canbe used. A desirable maximum temperature of the nematic phase isapproximately 70° C. or higher and a desirable minimum temperature ofthe nematic phase is approximately −10° C. or lower. The viscosity ofthe composition relates to the response time of the device. A shortresponse time is desirable to display moving images on the device.Accordingly, a small viscosity of the composition is desirable. A smallviscosity at a low temperature is more desirable.

TABLE 1 General Characteristics of a Liquid Crystal Composition and anAM Device General Characteristics of a General Characteristics of an AMNo Composition Device 1 Temperature range of a nematic Usabletemperature range is wide phase is wide 2 Viscosity is small¹⁾ Responsetime is short 3 Optical anisotropy is suitable Contrast ratio is large 4Dielectric anisotropy is Threshold voltage is low and positively ornegatively large electric power consumption is small Contrast ratio islarge 5 Specific resistance is large Voltage holding ratio is large anda contrast ratio is large 6 Stable to ultraviolet light and Service lifeis long heat ¹⁾A liquid crystal composition can be injected into aliquid crystal cell in a shorter period of time.

The optical anisotropy of the composition relates to the contrast ratioof the device. The product (Δn×d) of the optical anisotropy (Δn) of thecomposition and the cell gap (d) of the device is designed so as tomaximize the contrast ratio. A suitable value of the product depends onthe kinds of operating modes In a device having a mode such as TN, asuitable value is about 0.45 μm. In this case, a composition having alarge optical anisotropy is desirable for a device having a small cellgap. A large dielectric anisotropy in the composition contributes to alow threshold voltage, a small electric power consumption and a largecontrast ratio of the device. Accordingly, the large dielectricanisotropy is desirable. A large specific resistance of the compositioncontributes to a large voltage holding ratio and a large contrast ratioof the device. Accordingly, a composition having a large specificresistance is desirable at room temperature and also at a hightemperature close to the maximum temperature of a nematic phase in theinitial stage. A composition having a large specific resistance isdesirable at room temperature and also at a high temperature close tothe maximum temperature of a nematic phase after it has been used for along time. The stability of the composition to ultraviolet light andheat relates to the service life of the liquid crystal display device.In the case where the stability is high, the device has a long servicelife. These characteristics are desirable for an AM device used in aliquid crystal projector, a liquid crystal television and so forth.

In an AM device having the TN mode, an optically active compound ismixed into the composition for the purpose of inducing a helicalstructural and giving a twist angle in liquid crystals. A compositionhaving a positive dielectric anisotropy is used there. On the otherhand, a composition having a negative dielectric anisotropy is used foran AM device having a VA mode. A composition having a positive ornegative dielectric anisotropy is used for an AM device having an IPSmode. A composition having a positive or negative dielectric anisotropyis used for an AM device having a PSA mode. An example of liquid crystalcomposition having a positive dielectric anisotropy is disclosed in thefollowing patent document.

Conventional compositions are disclosed in the following patentdocument. No. 1: JP H6-200251 A (1994).

A desirable AM device has characteristics such as a wide temperaturerange in which the device can be used, a short response time, a largecontrast ratio, a low threshold voltage, a large voltage holding ratio,and a long service life. Even one millisecond shorter response time isdesirable. Thus, a composition having characteristics such as a highmaximum temperature of a nematic phase, a low minimum temperature of anematic phase, a small viscosity, a large optical anisotropy, a largedielectric anisotropy, a large specific resistance, a high stability toultraviolet light, and a high stability to heat is especially desirable.

SUMMARY OF THE INVENTION

The invention concerns a liquid crystal composition having a nematicphase that includes two components, wherein the first component is atleast one optically active compound selected from the group of compoundsrepresented by formula (1), the second component is at least onecompound selected from the group of compounds represented by formula(2), and concerns a liquid crystal display device containing thecomposition:

wherein R¹ and R⁴ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine; R² and R³ are each different and are alkyl having 1 to 12carbons or alkenyl having 2 to 12 carbons; ring A, ring B and ring C areeach independently 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,3,5-difluoro-1,4-phenylene or 2,5-pyrimidine; Z¹ and Z² are eachindependently a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy; X¹ and X² are each independently hydrogen orfluorine; Y¹ is fluorine, chlorine or trifluoromethoxy; and k and m areeach independently 0, 1, 2 or 3, and the sum of k and m is 3 or less.

When a combination of two or more compounds represented by formula (1)is used, they are desirable to have the same direction of twist fordecreasing the helical pitch and for adjusting the temperaturedependence in the composition. Incidentally, an optically activecompound having one direction of twist maybe combined with that havingthe reverse direction of twist for adjusting the length of the helicalpitch, temperature dependence or the like in the composition.

The invention also concerns a liquid crystal display device thatincludes the liquid crystal composition.

DETAILED DESCRIPTION OF THE INVENTION

The terms used in the specification and claims are defined as follows.The liquid crystal composition and the liquid crystal display device ofthe invention may occasionally be abbreviated to “the composition” and“the device,” respectively. A liquid crystal display device is a genericterm for a liquid crystal display panel and a liquid crystal displaymodule. The “liquid crystal compound” is a generic term for a compoundhaving a liquid crystal phase such as a nematic phase and a smecticphase, and also for a compound having no liquid crystal phases but beinguseful as a component of a composition. The useful compound has asix-membered ring such as 1,4-cyclohexylene and 1,4-phenylene, and arod-like molecular structure. An optically active compound or apolymerizable compound may occasionally be added to the composition.Even in the case where these compounds are liquid crystal compounds, thecompounds are classified as an additive herein. At least one compoundselected from the group of compounds represented by formula (1) mayoccasionally be abbreviated to “the compound (1).” “The compound (1)”means one compound, or two or more compounds represented by formula (1).The same rules apply to compounds represented by the other formulas.“Arbitrary” is used not only in cases when the position is arbitrary butalso in cases when the number is arbitrary. However, it is not used incases when the number is 0 (zero).

A higher limit of the temperature range of a nematic phase mayoccasionally be abbreviated to “the maximum temperature.” A lower limitof the temperature range of a nematic phase may occasionally beabbreviated to “the minimum temperature.” That “a specific resistance islarge” means that a composition has a large specific resistance at roomtemperature and also at a temperature close to the maximum temperatureof a nematic phase in the initial stage, and that the composition has alarge specific resistance at room temperature and also at a temperatureclose to the maximum temperature of a nematic phase even after it hasbeen used for a long time. That “a voltage holding ratio is large” meansthat a device has a large voltage holding ratio at room temperature andalso at a temperature close to the maximum temperature of a nematicphase in the initial stage, and that the device has a large voltageholding ratio at room temperature and also at a temperature close to themaximum temperature of a nematic phase even after it has been used for along time. When characteristics such as optical anisotropy areexplained, values which are obtained according to the measuring methodsdescribed in Examples will be used. A first component means onecompound, or two or more compounds. “A ratio of the first component”means the weight ratio (part by weight) of the first component when theweight of the liquid crystal composition excluding the first componentis set to 100 parts. “A ratio of the second component” means thepercentage by weight (% by weight) of the second component based on theweight of the liquid crystal composition excluding the first component.The same rules apply to “a ratio of a third component” and “a ratio of afourth component.” A ratio of an additive mixed into the compositionmeans the percentage by weight (% by weight) or weight parts per million(ppm) based on the total weight of the liquid crystal composition.

The symbol R¹ is used for a plurality of compounds in the chemicalformulas of component compounds. The meanings of two arbitrary R¹ maybeidentical or different in these compounds. In one case, for example, R¹of the compound (1) is ethyl and R¹ of the compound (1-1) is ethyl. Inanother case, R¹ of the compound (1) is ethyl and R¹ of the compound(1-1) is propyl. The same rule applies to the symbol R⁴, X¹ and soforth. In chemical formulas, “CL” stands for chlorine.

One of the advantages of the invention is to provide a liquid crystalcomposition that satisfies at least one of characteristics such as ahigh maximum temperature of a nematic phase, a low minimum temperatureof a nematic phase, a small viscosity, a large optical anisotropy, alarge dielectric anisotropy, a large specific resistance, a highstability to ultraviolet light and a high stability to heat. Anotheradvantage of the invention is to provide a liquid crystal compositionthat is suitably balanced regarding at least two of the characteristics.A further advantage of the invention is to provide a liquid crystaldisplay device that contains the liquid crystal composition. Anadditional advantage of the invention is to provide a liquid crystalcomposition that has a large optical anisotropy, a large dielectricanisotropy, a high stability to ultraviolet light and so forth, and isto provide an AM device that has a short response time, a large voltageholding ratio, a large contrast ratio, a long service life and so forth.

The liquid crystal composition of the invention satisfied at least onecharacteristic among the characteristics such as a high maximumtemperature of a nematic phase, a low minimum temperature of a nematicphase, a small viscosity, a large optical anisotropy, a large dielectricanisotropy, a large specific resistance, a high stability to ultravioletlight and a high stability to heat. The liquid crystal composition wassuitably balanced regarding at least two characteristics. The liquidcrystal display device contained the liquid crystal composition. Theliquid crystal composition had a large optical anisotropy, a largedielectric anisotropy, a high stability to ultraviolet light and soforth, and the AM device had a short response time, a large voltageholding ratio, a large contrast ratio, a long service life and so forth.

The invention includes the following items.

-   Item 1. A liquid crystal composition having a nematic phase that    includes two components, wherein the first component is at least one    optically active compound selected from the group of compounds    represented by formula (1), and the second component is at least one    compound selected from the group of compounds represented by formula    (2):

wherein R¹ and R⁴ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine; R² and R³ are each different and are alkyl having 1 to 12carbons or alkenyl having 2 to 12 carbons; ring A, ring B and ring C areeach independently 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,3,5-difluoro-1,4-phenylene or 2,5-pyrimidine; Z¹ and Z² are eachindependently a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy; X¹ and X² are each independently hydrogen orfluorine; Y¹ is fluorine, chlorine or trifluoromethoxy; and k and m areeach independently 0, 1, 2 or 3, and the sum of k and m is 3 or less.

-   Item 2. The liquid crystal composition according to item 1, wherein    the sum of the number of carbons in R² and R³ of formula (1) is in    the range of 3 to 10.-   Item 3. The liquid crystal composition according to item 1, wherein    the first component is at least one compound selected from the group    of compounds represented by formula (1-1):

wherein R¹ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine.

-   Item 4. The liquid crystal composition according to any one of items    1 to 3, wherein the second component further includes at least one    compound selected from the group of compounds represented by formula    (2-1) to formula (2-13):

wherein R⁴ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine; X¹, X², X³,X⁴, X⁵, X⁶, X⁷, X⁸ and X⁹ are each independently hydrogen or fluorine;and Y¹ is fluorine, chlorine or trifluoromethoxy.

-   Item 5. The liquid crystal composition according to item 4, wherein    the second component is at least one compound selected from the    group of compounds represented by formula (2-3).-   Item 6. The liquid crystal composition according to item 4, wherein    the second component is at least one compound selected from the    group of compounds represented by formula (2-5).-   Item 7. The liquid crystal composition according to item 4, wherein    the second component is at least one compound selected from the    group of compounds represented by formula (2-8).-   Item 8. The liquid crystal composition according to item 4, wherein    the second component is a mixture of at least one compound selected    from the group of compounds represented by formula (2-3) and at    least one compound selected from the group of compounds represented    by formula (2-8).-   Item 9. The liquid crystal composition according to item 4, wherein    the second component Is a mixture of at least one compound selected    from the group of compounds represented by formula (2-5) and at    least one compound selected from the group of compounds represented    by formula (2-8).-   Item 10. The liquid crystal composition according to any one of    items 1 to 9, wherein the ratio of the first component is in the    range of approximately 0.01 part to approximately 5 parts by weight    based on 100 parts by weight of the liquid crystal composition    excluding the first component.-   Item 11. The liquid crystal composition according to any one of    items 1 to 10, wherein the ratio of the second component is in the    range of approximately 5% to approximately 55% by weight based on    the weight of the liquid crystal composition excluding the first    component.-   Item 12. The liquid crystal composition according to any one of    items 1 to 11, wherein the composition further includes at least one    compound selected from the group of compounds represented by    formula (3) as a third component:

wherein R⁵ and R⁶ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine; ring D and ring E are each independently 1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene or2,5-difluoro-1,4-phenylene; Z³ is independently a single bond, ethyleneor carbonyloxy; and p is 1 or 2.

-   Item 13. The liquid crystal composition according to item 12,    wherein the third component is at least one compound selected from    the group of compounds represented by formula (3-1) to formula    (3-7):

wherein R⁵ and R⁶ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine.

-   Item 14. The liquid crystal composition according to item 13,    wherein the third component is at least one compound selected from    the group of compounds represented by formula (3-1).-   Item 15. The liquid crystal composition according to item 13,    wherein the third component is a mixture of at least one compound    selected from the group of compounds represented by formula (3-1)    and at least one compound selected from the group of compounds    represented by formula (3-5).-   Item 16. The liquid crystal composition according to item 13,    wherein the third component is a mixture of at least one compound    selected from the group of compounds represented by formula (3-1)    and at least one compound selected from the group of compounds    represented by formula (3-7).-   Item 17. The liquid crystal composition according to item 13,    wherein the third component is a mixture of at least one compound    selected from the group of compounds represented by formula (3-1),    at least one compound selected from the group of compounds    represented by formula (3-5), and at least one compound selected    from the group of compounds represented by formula (3-7).-   Item 18. The liquid crystal composition according to any one of    items 12 to 17, wherein the ratio of the third component is in the    range of approximately 35% to approximately 95% by weight based on    the weight of the liquid crystal composition excluding the first    component.-   Item 19. The liquid crystal composition according to any one of    items 1 to 18, wherein the composition further includes at least one    compound selected from the group of compounds represented by    formula (4) as a fourth component:

wherein R⁷ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine; ring F isindependently 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, 1,4-phenylene,2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,3,5-difluoro-1,4-phenylene or 2,5-pyrimidine; Z⁴ is independently asingle bond, ethylene or carbonyloxy; X¹⁰ and X¹¹ are each independentlyhydrogen or fluorine; Y² is fluorine, chlorine or trifluoromethoxy; andq is 1, 2 or 3.

-   Item 20. The liquid crystal composition according to item 19,    wherein the fourth component is at least one compound selected from    the group of compounds represented by formula (4-1) to formula    (4-11):

wherein R⁷ is an alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine.

-   Item 21. The liquid crystal composition according to item 20,    wherein the fourth component is at least one compound selected from    the group of compounds represented by formula (4-5).-   Item 22. The liquid crystal composition according to item 20,    wherein the fourth component is at least one compound selected from    the group of compounds represented by formula (4-7).-   Item 23. The liquid crystal composition according to item 20,    wherein the fourth component is at least one compound selected from    the group of compounds represented by formula (4-8).-   Item 24. The liquid crystal composition according to item 20,    wherein the fourth component is a mixture of at least one compound    selected from the group of the compounds represented by formula    (4-5) and at least one compound selected from the group of compounds    represented by formula (4-8).-   Item 25. The liquid crystal composition according to item 20,    wherein the fourth component is a mixture of at least one compound    selected from the group of the compounds represented by formula    (4-7) and at least one compound selected from the group of compounds    represented by formula (4-8).-   Item 26. The liquid crystal composition according to any one of    items 19 to 25, wherein the ratio of the fourth component is in the    range of approximately 5% to approximately 60% by weight based on    the weight of the liquid crystal composition excluding the first    component.-   Item 27. The liquid crystal composition according to any one of    items 1 to 26, wherein the maximum temperature of a nematic phase is    approximately 70° C. or higher, the optical anisotropy (25° C.) at a    wavelength of 589 nm is approximately 0.08 or more, and the    dielectric anisotropy (25° C.) at a frequency of 1 kHz is    approximately 2 or more.-   Item 28. A liquid crystal display device including the liquid    crystal composition according to any one of items 1 to 27.-   Item 29. The liquid crystal display device according to item 28,    wherein an operating mode of the liquid crystal display device is a    TN mode, an OCB mode, an IPS mode or a PSA mode, and a driving mode    of the liquid crystal display device is an active matrix mode.

The invention further includes the following items: (1) the compositiondescribed above that further includes an optically active compound; (2)the composition described above that further includes an additive, suchas an antioxidant, an ultraviolet light absorbent, an antifoaming agent,a polymerizable compound, and/or a polymerization initiator; (3) an AMdevice that includes the composition described above; (4) a devicehaving a mode of TN, ECB, OCB, IPS or PSA and including the compositiondescribed above; (5) a device having a transmission type and includingthe composition described above; (6) use of the composition describedabove as a composition having a nematic phase; and (7) use of thecomposition described above as an optically active composition.

The composition of the invention will be explained in the followingorder. First, the constitution of component compounds in the compositionwill be explained. Second, main characteristics of the componentcompounds and main effects of the compounds on the composition will beexplained. Third, a combination of components in the composition,desirable ratios of the component compounds and the basis thereof willbe explained. Fourth, a desirable embodiment of the component compoundswill be explained. Fifth, examples of the component compound will beshown. Sixth, additives that maybe mixed into the composition will beexplained. Seventh, methods for synthesizing the component compoundswill be explained. Last, use of the composition will be explained.

First, the constitution of component compounds in the composition willbe explained. The composition of the invention is classified into thecomposition A and the composition B. The composition A may furthercontain other liquid crystal compounds, an additive, an impurity and soforth. “The other liquid crystal compounds” are different from thecompound (1), the compound (2), the compound (3) and the compound (4).Such compounds are mixed into the composition for the purpose of furtheradjusting characteristics of the composition. Of the other liquidcrystal compounds, a smaller amount of cyano compound is more desirablein view of its stability to heat or ultraviolet light. A more desirableratio of the cyano compound is approximately 0% by weight. The additiveincludes an optically active compound other than the first component, anantioxidant, an ultraviolet light absorbent, a coloring matter, anantifoaming agent, a polymerizable compound and a polymerizationinitiator. The impurity is a compound and so forth contaminated in aprocess such as the synthesis of component compounds. Even in the casewhere the compound is a liquid crystal compound, it is classified as animpurity herein.

The composition B is essentially consisting of compounds selected fromthe group of the compound (1), the compound (2), the compound (3) andthe compound (4). The term “essentially” means that the composition maycontain an additive and an impurity, but does not contain other liquidcrystal compounds which are different from these compounds. Thecomposition B has a smaller number of components than the composition A.The composition B is preferable to the composition A in view of costreduction. The composition A is preferable to the composition B in viewof the fact that characteristics can be further adjusted by mixing theother liquid crystal compounds.

Second, main characteristics of the component compounds and main effectsof the compounds on the composition will be explained. The maincharacteristics of the component compounds are summarized in Table 2 onthe basis of the effects of the invention. In Table 2, the symbol Lstands for “large” or “high”, the symbol M stands for “medium.”, and thesymbol S stands for “small” or “low.” The symbols L, M and S areclassified on the basis of a qualitative comparison among the componentcompounds, and 0 (zero) means that “a value is nearly zero.”

TABLE 2 Characteristics of compounds Compounds Compound (2) Compound (3)Compound (4) Maximum S to M S to L M to L Temperature Viscosity M to L Sto M M to L Optical M to L S to L M to L Anisotropy Dielectric L 0 M toL Anisotropy Specific L L L Resistance

Main effects of the component compounds on the characteristics of thecomposition upon mixing the component compounds to the composition areas follows. The compound (2) increases the dielectric anisotropy. Thecompound (3) increases the maximum temperature or decreases theviscosity. The compound (4) decreases the minimum temperature andincreases the dielectric anisotropy.

Third, a combination of components in the composition, desirable ratiosof the component compounds and the basis thereof will be explained. Thecombination of the components in the composition is the first and secondcomponents, the first, second and third components, the first, secondand fourth components, and the first, second, third and fourthcomponents. A desirable combination of the components in the compositionare the first, second and third components.

A desirable ratio of the first component is approximately 0.01 part byweight or more, and 5 parts by weight or less. A more desirable ratio isin the range of approximately 0.05 part to approximately 3 parts byweight. An especially desirable ratio is in the range of approximately0.1 part to approximately 2 parts by weight.

A desirable ratio of the second component is approximately 5% by weightor more for increasing the dielectric anisotropy, and is approximately55% by weight or less for decreasing the viscosity. A more desirableratio is in the range of approximately 5% to approximately 50% byweight. An especially desirable ratio is in the range of approximately5% to approximately 45% by weight.

A desirable ratio of the third component is approximately 35% by weightor more for increasing the maximum temperature or decreasing theviscosity, and is approximately 95% by weight or less for increasing thedielectric anisotropy. A more desirable ratio is in the range ofapproximately 40% to approximately 90% by weight. An especiallydesirable ratio is in the range of approximately 45% to approximately85% by weight.

A desirable ratio of the fourth component is approximately 3% by weightor more for decreasing the minimum temperature and increasing thedielectric anisotropy, and is approximately 45% by weight or less fordecreasing the viscosity. A more desirable ratio is in the range ofapproximately 3% to approximately 40% by weight. An especially desirableratio is in the range of approximately 3% to approximately 35% byweight.

Fourth, a desirable embodiment of the component compounds will beexplained. R¹, R⁴, R⁵, R⁶ and R⁷ are each independently alkyl having 1to 12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, or alkenyl having 2 to 12 carbons in which arbitrary hydrogenis replaced by fluorine. Desirable R¹, R⁴, R⁶ or R⁷ is alkyl having 1 to12 carbons for increasing the stability to ultraviolet light or heat.Desirable R⁵ is alkenyl having 2 to 12 carbons for decreasing theminimum temperature or decreasing the viscosity. R² and R³ are eachindependently alkyl having 1 to 12 carbons or alkenyl having 2 to 12carbons. Desirable R² or R³ is alkyl having 1 to 12 carbons forincreasing the stability to ultraviolet light or heat.

Desirable alkyl is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptylor octyl. More desirable alkyl is ethyl, propyl, butyl, pentyl or heptylfor decreasing the viscosity.

Desirable alkoxy is methoxy, ethoxy, propoxy, butoxy, pentyloxy,hexyloxy or heptyloxy. More desirable alkoxy is methoxy or ethoxy fordecreasing the viscosity.

Desirable alkenyl is vinyl, 1-propenyl, 2-propenyl, 1-butenyl,2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl,1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl or 5-hexenyl. A moredesirable alkenyl is vinyl, 1-propenyl, 3-butenyl or 3-pentenyl fordecreasing the viscosity. A desirable configuration of —CH═CH— in thealkenyl depends on the position of the double bond. Trans is preferablein the alkenyl such as 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl,3-pentenyl and 3-hexenyl for decreasing the viscosity and for something.Cis is preferable in the alkenyl such as 2-butenyl, 2-pentenyl and2-hexenyl. In the alkenyl, straight-chain alkenyl is preferable tobranched-chain alkenyl.

Desirable examples of alkenyl in which arbitrary hydrogen is replaced byfluorine are 2,2-difluorovinyl, 3,3-difluoro-2-propenyl,4,4-difluoro-3-butenyl, 5,5-difluoro-4-pentenyl and6,6-difluoro-5-hexenyl. More desirable examples are 2,2-difluoro-vinyland 4,4-difluoro-3-butenyl for decreasing the viscosity.

Ring A, ring C and ring F are each independently 1,4-cyclohexylene,1,3-dioxane-2,5-diyl, 1,4-phenylene, 2-fluoro-1,4-phenylene,3-fluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene or 2,5-pyrimidine,wherein two arbitrary ring A may be identical or different when k is 2or 3, two arbitrary ring C may be identical or different when m is 2 or3, and two arbitrary ring F may be identical or different when q is 2 or3. Desirable ring A, ring C or ring F is 1,4-phenylene for increasingthe optical anisotropy. Ring B is 1,4-cyclohexylene,1,3-dioxane-2,5-diyl, 1,4-phenylene, 2-fluoro-1,4-phenylene,3-fluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene or 2,5-pyrimidine.Desirable ring B is 3,5-difluoro-1,4-phenylene for increasing theoptical anisotropy. Ring D and ring E are each independently1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene,3-fluoro-1,4-phenylene or 2,5-difluoro-1,4-phenylene, and two ring D maybe identical or different when p is 2. Desirable ring D or E is1,4-cyclohexylene for decreasing the viscosity or 1,4-phenylene forincreasing the optical anisotropy.

Z¹ and Z² are each independently a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy, wherein two arbitrary Z¹ may be identical ordifferent when k is 2 or 3, and two arbitrary Z¹ may be identical ordifferent when m is 2 or 3. Desirable Z¹ or Z² is a single bond fordecreasing the viscosity. Z³ is independently a single bond, ethylene orcarbonyloxy, wherein two Z³ maybe identical or different when p is 2.Desirable Z³ is a single bond for decreasing the viscosity. Z⁴ is asingle bond, ethylene or carbonyloxy, wherein two arbitrary Z⁴ may beidentical or different when q is 2 or 3. Desirable Z⁴ is a single bondfor decreasing the viscosity.

X¹, X², X³, X⁴, X⁵, X⁶, X⁷, X⁸, X⁹, X¹⁰ and X¹¹ are each independentlyhydrogen or fluorine. Desirable X¹, X², X³, X⁴, X⁵, X⁶, X⁷, X⁸, X⁹, X¹⁰or X¹¹ is fluorine for increasing the dielectric anisotropy.

Y¹ or Y² is fluorine, chlorine or trifluoromethoxy. Desirable Y¹ or Y²is fluorine for decreasing the minimum temperature.

k and m are each independently 0, 1, 2 or 3, and the sum of k and m is 3or less. Desirable k is 2 for increasing the maximum temperature.Desirable m is 0 for decreasing the minimum temperature. p is 1 or 2.Desirable p is 1 for decreasing the viscosity. q is independently 1, 2or 3. Desirable q is 2 for decreasing the minimum temperature.

Fifth, examples of the component compound will be shown. In thedesirable compounds described below, R⁸, R⁹ and R¹³ are straight-chainalkyl having 1 to 12 carbons. R¹⁰ is straight-chain alkyl having 1 to 12carbons or straight-chain alkoxy having 1 to 12 carbons. R¹¹ and R¹² areeach independently straight-chain alkyl having 1 to 12 carbons orstraight-chain alkenyl having 2 to 12 carbons. With regard to theconfiguration of 1,4-cyclohexylene in these compounds, trans ispreferable to cis for increasing the maximum temperature.

Desirable compound (1) is the compound (1-1-1). Desirable compound (2)are the compounds (2-1-1) to (2-8-1), the compounds (2-9-1) to (2-9-2),the compounds (2-10-1) to (2-10-3), the compounds (2-11-1) to (2-11-2),the compound (2-12-1), the compounds (2-13-1) to (2-13-2) and thecompounds (2-14-1) to (2-18-1). More desirable compound (2) are thecompound (2-2-1), the compound (2-3-1), the compound (2-5-1) and thecompound (2-8-1). Especially desirable compound (2) are the compound(2-3-1), the compound (2-5-1) and the compound (2-8-1). Desirablecompound (3) are the compounds (3-1-1) to (3-7-1). More desirablecompound (3) are the compound (3-1-1), the compound (3-5-1) and thecompound (3-7-1). Desirable compound (4) are the compounds (4-1-1) to(4-11-1) and the compounds (4-12-1) to (4-15-1). More desirable compound(4) are the compound (4-5-1), the compound (4-7-1) and the compound(4-8-1).

Sixth, additives which may be mixed into the composition will beexplained. The additives include an optically active compound other thanthe first component, an antioxidant, an ultraviolet light absorbent, acoloring matter, an antifoaming agent, a polymerizable compound and apolymerization initiator. Examples of the optically active compoundinclude the compounds (5-1) to (5-4). A desirable ratio of the opticallyactive compound is approximately 5% by weight or less, and a moredesirable ratio is in the range of approximately 0.01% to approximately2% by weight.

When an optically active compound other than the first component isadded, it is desirable to have the same direction of twist as that ofthe first component, namely the compound (1), for decreasing the helicalpitch of the composition, for adjusting the temperature dependence orfor something. Incidentally, an optically active compound having onedirection of twist maybe combined with that having the reverse directionof twist for adjusting the length of the helical pitch, temperaturedependence or the like in the composition.

An antioxidant is mixed into the composition in order to prevent adecrease in specific resistance caused by heating in air, or to maintaina large voltage holding ratio at room temperature and also at atemperature close to the maximum temperature of a nematic phase evenafter the device has been used for a long time.

Desirable examples of the antioxidant include the compound (6) wherein nis an integer of from 1 to 9. In the compound (6), desirable n is 1, 3,5, 7 or 9. A more desirable n is 1 or 7. The compound (6) wherein n is 1is effective in preventing a decrease of the specific resistance causedby heating in air because it has a large volatility. The compound (6)wherein n is 7 is effective in maintaining a large voltage holding ratioat room temperature and also at a temperature close to the maximumtemperature of a nematic phase even after the device has been used for along time, because it has a small volatility. A desirable ratio of theantioxidant is approximately 50 ppm or more for achieving its effect andis approximately 600 ppm or less for avoiding a decrease of the maximumtemperature or avoiding an increase of the minimum temperature. A moredesirable ratio is in the range of approximately 100 ppm toapproximately 300 ppm.

Desirable examples of the ultraviolet light absorbent include abenzophenone derivative, a benzoate derivative and a triazolederivative. A light stabilizer such as an amine having steric hindranceis also desirable. A desirable ratio of the ultraviolet light absorbentand the light stabilizer is approximately 50 ppm or more for achievingits effect and is approximately 10,000 ppm or less for avoiding adecrease of the maximum temperature or avoiding an increase of theminimum temperature. A more desirable ratio is in the range ofapproximately 100 ppm to approximately 10,000 ppm.

A dichroic dye such as an azo dye or an anthraquinone dye is mixed intothe composition for adjusting to a device having a guest host (GH) mode.A desirable ratio of the coloring matter is in the range ofapproximately 0.01% to approximately 10% by weight. An antifoaming agentsuch as dimethyl silicone oil or methyl phenyl silicone oil is mixedinto the composition for preventing foam formation. A desirable ratio ofthe antifoaming agent is approximately 1 ppm or more for achieving itseffect and is approximately 1,000 ppm or less for avoiding a poordisplay. A more desirable ratio is in the range of approximately 1 ppmto approximately 500 ppm.

A polymerizable compound is mixed into the composition for adjusting toa device having a PSA (polymer sustained alignment) mode. Desirableexamples of the polymerizable compound include compounds having apolymerizable group, such as acrylates, methacrylates, vinyl compounds,vinyloxy compounds, propenyl ethers, epoxy compounds (oxirane, oxetane)and vinyl ketones. Especially desirable examples of the polymerizablecompound are acrylate derivatives or methacrylate derivatives. Adesirable ratio of the polymerizable compound is approximately 0.05% byweight or more for achieving its effect and is approximately 10% byweight or less for avoiding a poor display. A more desirable ratio is inthe range of approximately 0.1% to approximately 2% by weight. Thepolymerizable compound is polymerized on irradiation with ultravioletlight or the like preferably in the presence of a suitable initiatorsuch as a photopolymerization initiator. Suitable conditions forpolymerization, suitable types of the initiator and suitable amountsthereof are known to a person skilled in the art and are disclosed inthe literature. For example, Irgacure 651 (registered trademark),Irgacure 184 (registered trademark) or Darocure 1173 (registeredtrademark) (Ciba Japan K K.) which is a photoinitiator, is suitable forradical polymerization. The polymerizable compound includes thephotopolymerization initiator preferably in the range of, approximately0.1% to approximately 5% by weight, and most preferably in the range ofapproximately 1% to approximately 3% by weight.

Seventh, methods for synthesizing the component compounds will beexplained. These compounds can be synthesized by known methods. Thesynthetic methods will be exemplified as follows. The compound (1-1-1)is synthesized by a method described in JP H6-200251 A (1994). Thecompound (2-3-1) and the compound (2-8-1) are synthesized by a methoddescribed in JP 1-110-251186 A (1998). The compound (3-1-1) and thecompound (3-5-1) are synthesized by the method described in the JPH4-30382 (1992). The compound (4-5-1) and the compound (4-8-1) aresynthesized by the method described in JP H2-233626 (1990). Anantioxidant is commercially available. The compound of formula (6),wherein n is 1, is available from Sigma-Aldrich Corporation. Thecompound of formula (6), wherein n is 7, is synthesized according to themethod described in U. S. Pat. No. 3,660,505.

Compounds of which the synthetic methods were not described above can besynthesized according to the methods described in books such as ORGANICSYNTHESES (John Wiley & Sons, Inc.), ORGANIC REACTIONS (John Wiley &Sons, Inc.), COMPREHENSIVE ORGANIC SYNTHESIS (Pergamon Press), and NEWEXPERIMENTAL CHEMISTRY COURSE (Shin Jikken Kagaku Kouza, in Japanesetitle) (Maruzen, Inc.). The composition is prepared according to knownmethods using the compounds thus obtained. For example, the componentcompounds are mixed and dissolved in each other by heating.

Last, use of the composition will be explained. Most of the compositionshave a minimum temperature of approximately −10° C. or lower, a maximumtemperature of approximately 70° C. or higher, and an optical anisotropyin the range of approximately 0.07 to approximately 0.20. The devicecontaining the composition has a large voltage holding ratio. Thecomposition is suitable for an AM device. The composition is suitableespecially for an AM device having a transmission type. The compositionhaving an optical anisotropy in the range of approximately 0.08 toapproximately 0.25 and the composition having an optical anisotropy evenin the range of approximately 0.10 to approximately 0.30 may be preparedby controlling the ratios of the component compounds or by mixing otherliquid crystal compounds. The composition can be used as an opticallyactive composition.

The composition can be used for an AM device. It can also be used for aPM device. The composition can also be used for the AM device and the PMdevice having a mode such as PC, TN, STN, ECB, OCB, IPS, VA or PSA. Itis especially desirable to use the composition for the AM device havingthe TN, OCB or IPS mode. These devices may be of a reflection type, atransmission type or a semi-transmission type. It is desirable to usethe composition for a device having the transmission type. It can alsobe used for an amorphous silicon-TFT device or a polycrystal silicon-TFTdevice. The composition is also usable for a nematic curvilinear alignedphase (NCAA) device prepared by microcapsulating the composition, andfor a polymer dispersed (PD) device in which a three dimensional networkpolymer is formed in the composition.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the invention and specificexamples provided herein without departing from the spirit or scope ofthe invention. Thus, it is intended that the invention covers themodifications and variations of this invention that come within thescope of any claims and their equivalents.

The following examples are for illustrative purposes only and are notintended, nor should they be interpreted to, limit the scope of theinvention.

Examples

A composition and a compound were a subject for measurement in order toevaluate characteristics of the composition and the compound to beincluded in the composition. When the subject for measurement was acomposition, the composition itself was measured as a sample, and thevalue obtained was described here. When the subject for measurement wasa compound, a sample for measurement, was prepared by mixing thecompound (15% by weight) and mother liquid crystals (85% by weight).Characteristic values of the compound were calculated from valuesobtained by measurement, according to a method of extrapolation. Thatis: (extrapolated value)=[(measured value of a sample formeasurement)−0.85×(measured value of mother liquid crystals)]/0.15. Whena smectic phase (or crystals) separated out at this ratio at 25° C., theratio of the compound and the mother liquid crystals was changed step bystep in the order of (10% by weight/90% by weight), (5% by weight/95% byweight), (1% by weight/99% by weight). Values of the maximumtemperature, the optical anisotropy, the viscosity and the dielectricanisotropy with regard to the compound were obtained by theextrapolation.

The components of the mother liquid crystals were as follows. The ratioof each component is expressed in percentage by weight.

Characteristics were measured according to the following methods. Mostmethods are described in the Standard of Electronic IndustriesAssociation of Japan, EIAJ•ED-2521A, or those with some modifications.

Direction of Twist regarding Helix: A composition was prepared by addinga sample (1 part by weight) to mother liquid crystals (100 parts byweight) and the helical pitch (P₁) was measured. The standard sample ofan optically active compound having a right-handed twist was added tothe mother liquid crystals, giving another composition. The amount ofthe standard sample was predetermined on the basis of calculation inorder that the degree of the helical pitch (P₂) of the composition wasthe same with that of P₁. Then, these compositions were mixed in equalportions and the helical pitch (P_(mix)) was measured. The sample wasdetermined to have a right-handed twist when the value of P_(mix) waslocated between values of P₁ and P₂, and a left-handed twist when thevalue of P_(mix) was substantially greater than that of P₁ (or P₂).

The standard optically active compound was as follows.

Maximum Temperature of Nematic Phase (NI; ° C.): A sample was placed ona hot plate in a melting point apparatus equipped with a polarizingmicroscope and was heated at the rate of 1° C. per minute. Temperaturewas measured when part of the sample began to change from a nematicphase to an isotropic liquid. A higher limit of the temperature range ofa nematic phase may occasionally be abbreviated to “the maximumtemperature.”

Minimum Temperature of Nematic Phase (T_(c); ° C.): A sample having anematic phase was put in glass vials and then kept in freezers attemperatures of 0° C., −10° C., −20° C., −30° C. and −40° C. for 10days, and then the liquid crystal phases were observed. For example,when the sample remained the nematic phase at −20° C. and changed tocrystals or a smectic phase at −30° C., T_(c) was expressed as ≦−20° C.A lower limit of the temperature range of a nematic phase mayoccasionally be abbreviated to “the minimum temperature.”

Viscosity (bulk viscosity; η; measured at 20° C.; mPa·s): Viscosity wasmeasured by use of an E-type viscometer.

Viscosity (rotational viscosity; γ1; measured at 25° C.; mPa·s):Measurement was carried out according to the method described in M.Imai, et al., Molecular Crystals and Liquid Crystals, Vol. 259, 37(1995). A sample was poured into a TN device having a twist angle of 0degrees and the distance between two glass substrates (cell gap) of 5μm. The TN device was impressed with a voltage stepwise with anincrement of 0.5 volt in the range of 16 to 19.5 volts. After a periodof 0.2 second without impressed voltage, voltage impress was repeatedunder the conditions of only one rectangular wave (rectangular pulse;0.2 second) and no voltage impressed (2 seconds). The peak current andthe peak time of the transient current generated by the voltageimpressed were measured. The value of rotational viscosity was obtainedfrom the measured values and the calculating equation (8) in page 40 ofthe paper presented by M. Imai, et al. The value of dielectricanisotropy necessary for this calculation was obtained by use of thedevice that had been used for the present measurement of rotationalviscosity, according to the method that will be described below.

Optical Anisotropy (refractive index anisotropy; Δn; measured at 25° C.): Measurement was carried out by use of an Abbe refractometer with apolarizing plate mounted on the ocular, on irradiation with light at awavelength of 589 nm. The surface of the main prism was rubbed in onedirection, and then a sample was dropped on the main prism. A refractiveindex (n∥) was measured when the direction of polarized light wasparallel to that of the rubbing. A refractive index (n⊥) was measuredwhen the direction of polarized light was perpendicular to that of therubbing. The value of optical anisotropy was calculated from theequation: Δn=n∥−n⊥.

Dielectric Anisotropy (Δε; measured at 25° C.): A sample was poured intoa TN device having the distance between two glass substrates (cell gap)of 9 μm and a twist angle of 80 degrees. Sine waves (10 V, 1 kHz) wereimpressed onto this device, and a dielectric constant (ε∥ in a majoraxis direction of liquid crystal molecules was measured after 2 seconds.Sine waves (0.5 V, 1 kHz) were impressed onto the device and adielectric constant (ε⊥) in a minor axis direction of a liquid crystalmolecule was measured after 2 seconds. The value of dielectricanisotropy was calculated from the equation: Δε=ε∥−ε⊥.

Threshold Voltage (Vth; measured at 25° C.; V): Measurement was carriedout with an LCD evaluation system Model LCD-5100 made by OtsukaElectronics Co., Ltd. The light source was a halogen lamp. A sample waspoured into a TN device having a normally white mode, in which thedistance between two glass substrates (cell gap) was about 0.45/Δn (μm)and a twist angle was 80 degrees. Voltage to be impressed onto thedevice (32 Hz, rectangular waves) was increased stepwise in 0.02 Vincrements from 0 V up to 10 V. During the increase, the device wasirradiated with light in the perpendicular direction, and the amount oflight passing through the device was measured. A voltage-transmittancecurve was prepared, in which the maximum amount of light corresponded to100% transmittance and the minimum amount of light corresponded to 0%transmittance. The threshold voltage was voltage at 90% transmittance.

Voltage Holding Ratio (VHR-1; measured at 25° C.; %): A TN device usedfor measurement had a polyimide-alignment film, and the distance betweentwo glass substrates (cell gap) was 5 μm. A sample was poured into thedevice, and then the device was sealed with an adhesive polymerizable onirradiation with ultraviolet light. The TN device was impressed andcharged with pulse voltage (60 microseconds at 5 V). A decreasingvoltage was measured for 16.7 milliseconds with a high-speed voltmeter,and the area A between a voltage curve and a horizontal axis in a unitcycle was obtained. The area B was an area without the decrease. Thevoltage holding ratio was a percentage of the area A to the area B.

Voltage Holding Ratio (VHR-2; measured at 80° C.; %): A TN device usedfor measurement had a polyimide-alignment film, and the distance betweentwo glass substrates (cell gap) was 5 μm. A sample was poured into thedevice, and then the device was sealed with an adhesive polymerizable onirradiation with ultraviolet light. The TN device was impressed andcharged with pulse voltage (60 microseconds at 5 V). A decreasingvoltage was measured for 16.7 milliseconds with a high-speed voltmeter,and the area A between a voltage curve and a horizontal axis in a unitcycle was obtained. The area B was an area without the decrease. Thevoltage holding ratio was a percentage of the area A to the area B.

Voltage Holding Ratio (VHR-3; measured at 25° C.; %): A voltage holdingratio was measured after irradiation with ultraviolet light, evaluatingstability to ultraviolet light. A composition having a large VHR-3 has ahigh stability to ultraviolet light. A TN device used for measurementhad a polyimide-alignment film and the cell gap was 5 μm. A sample waspoured into the device, and then the device was irradiated with lightfor 20 minutes. The light source was an ultra high-pressure mercury lampUSH 500D (produced by Ushio, Inc.), and the distance between the deviceand the light source was 20 cm. In the measurement of VHR-3, adecreasing voltage was measured for 16.7 milliseconds. The value ofVHR-3 is preferably 90% or more, and more preferably 95% or more.

Voltage Holding Ratio (VHR-4; measured at 25° C.; %): A TN device intowhich a sample was poured was heated in a constant-temperature bath at80° C. for 500 hours, and then the voltage holding ratio was measured,evaluating stability to heat. A composition having a large VHR-4 has ahigh stability to heat. In the measurement of VHR-4, a decreasingvoltage was measured for 16.7 milliseconds.

Response Time (τ; measured at 25° C.; millisecond): Measurement wascarried out with an LCD evaluation system Model LCD-5100 made by OtsukaElectronics Co., Ltd. The light source was a halogen lamp. The low-passfilter was set at 5 kHz. A sample was poured into a TN device having anormally white mode, in which the distance between two glass substrates(cell gap) was 5.0 μm and a twist angle was 80 degrees. Rectangularwaves (60 Hz, 5 V, 0.5 second) were impressed to the TN device. Thedevice was simultaneously irradiated with light in the perpendiculardirection, and the amount of light passing through the device wasmeasured. The maximum amount of light corresponded to 100%transmittance, and the minimum amount of light corresponded to 0%transmittance. A rise time (τr: rise time; milliseconds) was the periodof time required for the change from 90% to 10% transmittance. A falltime (τf: fall time; millisecond) was the period of time required forthe change from 10% to 90% transmittance. The response time was the sumof the rise time and the fall time thus obtained.

Specific resistance (ρ; measured at 25° C.; Ω cm): A sample of 1.0milliliters was poured into a vessel equipped with electrodes. DCvoltage (10 V) was impressed to the vessel, and the DC current wasmeasured after 10 seconds. The specific resistance was calculatedaccording to the following equation. (specificresistance)=[(voltage)×(electric capacity of vessel)]/[(DCcurrent)×(dielectric constant in a vacuum)].

Helical pitch (P; measured at room temperature; μm): The helical pitchwas measured according to the wedge method (page 196 of LIQUID CRYSTALHANDBOOK, Maruzen, Inc., 2000)). After a sample had been injected into awedge-shaped cell and the cell had been allowed to stand at roomtemperature for 2 hours, the interval (d2-d1) of disclination lines wasobserved with a polarizing microscope (Nikon Corporation, Model MM-40/60series). The helical pitch (P) was calculated from the followingequation, wherein θ was defined as the angle of the wedge cell.P=2×(d2-d1)×tan θ.

Gas chromatographic analysis: A Gas Chromatograph Model GC-14B made byShimadzu Corporation was used for measurement. The carrier gas washelium (2 milliliters per minute). The evaporator and the detector (FID)were set up at 280° C. and 300° C., respectively. A capillary columnDB-1 (length 30 meters, bore 0.32 millimeter, film thickness 0.25micrometer, dimethylpolysiloxane as the stationary phase, non-polar)made by Agilent Technologies, Inc. was used for the separation ofcomponent compounds. After the column had been kept at 200° C. for 2minutes, it was further heated to 280° C. at the rate of 5° C. perminute. A sample was prepared in an acetone solution (0.1% by weight),and 1 microliter of the solution was injected into the evaporator. Arecorder used was a Model C-R5A Chromatopac Integrator made by ShimadzuCorporation or its equivalent. A gas chromatogram obtained showed theretention time of peaks and the peak areas corresponding to thecomponent compounds.

Solvents for diluting the sample may also be chloroform, hexane, and soforth. The following capillary columns may also be used in order toseparate the component compounds: HP-1 made by Agilent Technologies Inc.(length 30 meters, bore 0.32 millimeter, film thickness 0.25micrometer), Rtx-1 made by Restek Corporation (length 30 meters, bore0.32 millimeter, film thickness 0.25 micrometer), and BP-1 made by SGEInternational Pty. Ltd. (length 30 meters, bore 0.32 millimeter, filmthickness 0.25 micrometer). A capillary column CBP1-M50-025 (length 50meters, bore 0.25 millimeter, film thickness 0.25 micrometer) made byShimadzu Corporation may also be used for the purpose of avoiding anoverlap of peaks of the compounds.

The ratio of the liquid crystal compound included in the composition maybe calculated according to the following method. The liquid crystalcompounds are detected by use of a gas chromatograph. The ratio of peakareas in the gas chromatogram corresponds to the ratio (in moles) of theliquid crystal compounds. When the capillary columns described above areused, the correction coefficient of respective liquid crystal compoundsmay be regarded as 1 (one). Accordingly, the ratio (% by weight) of theliquid crystal compound can be calculated from the ratio of peak areas.

The invention will be explained in detail by way of Examples. Theinvention is not limited by Examples described below. The compoundsdescribed in Comparative Examples and Examples were expressed as symbolsaccording to the definition in the following Table 3. In Table 3, theconfiguration of 1,4-cyclohexylene is trans. A parenthesized number nextto the symbolized compound in Examples correspond to the compound'snumber. The symbol (−) means other liquid crystal compounds. Ratios(percentage) of liquid crystal compounds mean the percentages by weight(% by weight) based on the total weight of the liquid crystalcomposition. The liquid crystal composition further includes animpurity. Last, characteristics of the composition are summarized.

TABLE 3 Method of Description of Compound using Symbols R—(A₁)—Z₁— . . .—Z_(n)—(A_(n))—R′ Symbol 1) Left Terminal Group R— C_(n)H_(2n+1)— n-C_(n)H_(2n+1)O— nO— C_(m)H_(2m+1)OC_(n)H_(2n)— mOn- CH₂═CH— V—C_(n)H_(2n+1)—CH═CH— nV— CH₂═CH—C_(n)H_(2n)— Vn-C_(m)H_(2m+1)—CH═CH—C_(n)H_(2n)— mVn- CF₂═CH— VFF— CF₂═CH—C_(n)H_(2n)—VFFn- 2) Right Terminal Group —R′ —C_(n)H_(2n+1) -n —OC_(n)H_(2n+1) —On—CH═CH₂ —V —CH═CH—C_(n)H_(2n+1) —Vn —C_(n)H_(2n)—CH═CH₂ -nV —CH═CF₂ —VFF—F —F —Cl —CL —OCF₃ —OCF3 —CN —C 3) Bonding Group —Z_(n)— —C₂H₄— 2 —COO—E —CH═CH— V —C≡C— T —CF₂O— X —CH═CH—CF₂O— VX 4) Ring Structure —A_(n)—

H

B

B(F)

B(2F)

B(F,F)

B(2F,5F)

Py

dh

G 5) Example of Description Example 1. 3-BB(F)B(F,F)—F

Example 2. V—HH-3

Example 3. 3-HHB-1

Example 4. 3-BB(F,F)XB(F)—OCF3

Comparative Example 1

Example 1 was selected from compositions disclosed in JP H6-200251 A(1994) for comparison. The basis for the selection was because thecomposition contained the compound (1-1-1) and the compound (4). Thecomposition had the following components and characteristics. Sincethere was no description of response time (τ), this composition wasprepared and the response time was measured according to the methoddescribed above.

2-HHB(F)-F (4) 33.4% 3-HHB(F)-F (4) 33.3% 5-HHB(F)-F (4) 33.3%

One part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

VHR-1=98.5%; VHR-2=98.4%; T=28.5 ms; P=25.1 μm.

Comparative Example 2

Example 4 was selected from compositions disclosed in JP H6-200251 A(1994) for comparison. The basis for the selection was because thecomposition contained the compound (1-1-1) and the compound (4). Thecomposition had the following components and characteristics. Sincethere was no description of response time (τ), this composition wasprepared and the response time was measured according to the methoddescribed above.

5-HB-OCF3 (4)   9% 2-HHB(F)-F (4) 16.7%  3-HHB(F)-F (4) 16.7% 5-HHB(F)-F (4) 16.6%  2-H2HB(F)-F (4) 8.4% 3-H2HB(F)-F (4) 4.2%5-H2HB(F)-F (4) 8.4% 2-HBB(F)-F (4)   5% 3-HBB(F)-F (4)   5% 5-HBB(F)-F(4)  10%

0.3 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=86.0° C.; Δn=0.088; τ=26.9 ms; P=82.0 μm.

Example 1

3-BB(F,F)XB(F,F)-F (2-3-1) 8% 5-BB(F)B(F,F)XB(F)B(F,F)-F (2-13-2) 3%3-BB(F,F)XB(F)-F (2-15-1) 12%  V-HH-3 (3-1-1) 33%  1V-HH-3 (3-1-1) 10% V2-BB-1 (3-3-1) 4% 3-HHEH-5 (3-4-1) 4% 2-BB(F)B-3 (3-7-1) 10% 1-BB(F)B-2V (3-7-1) 6% 3-HHEB(F,F)-F (4-12-1) 10% 

One part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=75.2° C.; Tc≦−20° C.; Δn=0.118; Δε=4.3; Vth=1.90 V; η]=13.5 mPa·s;γ1=58.2 mPa·s; τ=9.8 ms; VHR-1=98.6%; VHR-2=98.3%; P=20.4 μm.

Example 2

3-BB(F,F)XB(F,F)-F (2-3-1) 13% 4-BB(F)B(F,F)XB(F,F)-F (2-8-1)  6% V-HH-3(3-1-1) 42% 1V-HH-3 (3-1-1)  4% V-HHB-1 (3-5-1) 10% 2-BB(F)B-3 (3-7-1)10% 2-BB(F)B-5 (3-7-1) 10% 3-HHBB(F,F)-F (4-10-1)  5%

0.5 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=75.6° C.; Tc≦−20° C.; Δn=0.118; Δε=3.9; Vth=2.18 V; η=11.5 mPa·s;γ1=48.1 mPa·s; τ=7.9 ms; VHR-1=99.3%; VHR-2=99.0%; P=41.1 μm.

Example 3

3-BB(F,F)XB(F,F)-F (2-3-1) 9% 3-BB(F)B(F,F)XB(F,F)-F (2-8-1) 2%4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 7% V-HH-3 (3-1-1) 48% V2-BB-1 (3-3-1) 5%1-BB(F)B-2V (3-7-1) 8% 2-BB(F)B-2V (3-7-1) 10% 3-BB(F)B-2V (3-7-1) 11%

0.5 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=71.6° C.; Tc≦−20° C.; Δn=0.137; Δε=4.0; Vth=2.25 V; η=12.3 mPa·s;γ1=52.8 mPa·s; τ=8.8 ms; VHR-1=99.2%; VHR-2=98.6%; P=40.3 μm.

Example 4

4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 8% 5-PyB(F)B(F,F)XB(F)B(F,F)-F (2-18-1)3% V-HH-3 (3-1-1) 40% 1V-HH-3 (3-1-1) 10% V-HHB-1 (3-5-1) 10% 3-HB-CL(4-1-1) 8% 3-HHB-CL (4-4-1) 6% 3-PyBB-F (4-9-1) 3% 4-PyBB-F (4-9-1) 3%5-PyBB-F (4-9-1) 3% 3-HHBB(F,F)-F (4-10-1) 6%

One part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=89.2° C.; Tc≦−20° C.; Δn=0.105; Δε=3.8; Vth=2.55 V; η=13.6 mPa·s;γ1=55.3 mPa·s; τ=9.6 ms; VHR-1=98.0%; VHR-2=97.6%; P=20.8 μm.

Example 5

3-BB(F,F)XB(F,F)-F (2-3-1) 20% V-HH-3 (3-1-1) 38% 1V-HH-3 (3-1-1) 6%V-HHB-1 (3-5-1) 12% 2-BB(F)B-3 (3-7-1) 10% 2-BB(F)B-5 (3-7-1) 9%3-HHBB(F,F)-F (4-10-1) 5%

0.8 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=72.1° C.; Tc≦−20° C.; Δn=0.114; Δε=3.9; Vth=2.31 V; η=10.6 mPa·s;γ1=45.9 mPa·s; τ=7.7 ms; VHR-1=99.1%; VHR-2=98.5%; P=26.6 μm.

Example 6

3-BB(F,F)XB(F,F)-F (2-3-1) 13% 5-HBB(F)B(F,F)XB(F,F)-F (2-10-3) 3%5-BB(F)B(F,F)XB(F)B(F)-OCF3 (2-13-1) 3% VFF-HH-3 (3-1) 9% V-HH-3 (3-1-1)39% 1V-HH-3 (3-1-1) 10% V-HHB-1 (3-5-1) 6% V2-HHB-1 (3-5-1) 5%3-HHB(F,F)-F (4-5-1) 6% 3-HBB-F (4-6-1) 6%

0.5 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=75.5° C.; Tc≦−20° C.; Δn=0.098; Δε=4.2; Vth=2.12 V; η=12.9 mPa·s;γ1=53.1 mPa·s; τ=8.8 ms; VHR-1=99.2%; VHR-2=98.6%; P=40.6 μm.

Example 7

3-BB(F,F)XB(F,F)-F (2-3-1) 14% 3-BB(F)B(F,F)XB(F,F)-F (2-8-1) 2%4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 9% 5-BB(F)B(F,F)XB(F,F)-F (2-8-1) 5%V-HH-3 (3-1-1) 48% V-HHB-1 (3-5-1) 8% 1-BB(F)B-2V (3-7-1) 6% 2-BB(F)B-2V(3-7-1) 8%

0.4 part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=71.2° C.; Tc≦−20° C.; Δn=0.120; Δε=5.5; Vth=1.68 V; η=11.8 mPa·s;γ1=49.8 mPa·s; τ=8.6 ms; VHR-1=99.2%; VHR-2=98.9%; P=47.1 μm.

Example 8

3-BB(F,F)XB(F,F)-F (2-3-1) 4% 3-BB(F)B(F,F)XB(F,F)-F (2-8-1) 2%4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 5% 5-BB(F)B(F,F)XB(F,F)-F (2-8-1) 5%V-HH-3 (3-1-1) 44% 1V-HH-3 (3-1-1) 8% V-HHB-1 (3-5-1) 3% V2-HHB-1(3-5-1) 3% 1-BB(F)B-2V (3-7-1) 4% 2-BB(F)B-2V (3-7-1) 8% 3-BB(F)B-2V(3-7-1) 9% 3-BB(F)B(F,F)-F (4-8-1) 5%

One part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=79.6° C.; Tc≦−20° C.; Δn=0.126; Δε=4.0; Vth=2.35 V; η=11.0 mPa·s;γ1=48.6 mPa·s; τ=8.1 ms; VHR-1=98.9%; VHR-2=98.4%; P=21.6 μm.

Example 9

3-BB(F,F)XB(F,F)-F (2-3-1) 10% 5-HBB(F)B(F,F)XB(F,F)-F (2-10-2) 3%5-BB(F)B(F)B(F,F)XB(F)-F (2-11-1) 3% 3-HHXB(F)-OCF3 (2-14-1) 8% V-HH-3(3-1-1) 36% 1V-HH-3 (3-1-1) 9% V2-BB-1 (3-3-1) 3% 1-BB(F)B-2V (3-7-1) 8%2-BB(F)B-2V (3-7-1) 6% 3-BB(F)B-2V (3-7-1) 5% 3-HBB(F,F)-F (4-7-1) 6%3-HBEB(F,F)-F (4-13-1) 3%

0.4 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=73.2° C.; Tc≦−20° C.; Δn=0.120; Δε=4.3; Vth=2.00 V; η=13.6 mPa·s;γ1=55.8 mPa·s; τ=9.7 ms; VHR-1=99.0%; VHR-2=98.6%; P=48.1 μm.

Example 10

3-BB(F,F)XB(F,F)-F (2-3-1) 7% 4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 5% V-HH-3(3-1-1) 46% 1V-HH-3 (3-1-1) 10% V-HHB-1 (3-5-1) 11% V2-HHB-1 (3-5-1) 4%2-BB(F)B-3 (3-7-1) 9% 2-BB(F)B-5 (3-7-1) 3% 3-HBB(F,F)-F (4-7-1) 5%

0.5 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=75.1° C.; Tc≦−20° C.; Δn=0.098; Δε=2.5; Vth=2.87 V; η=9.37 mPa·s;γ1=38.4 mPa·s; τ=6.5 ms; VHR-1=99.2%; VHR-2=98.8%; P=42.1 μm.

Example 11

3-BB(F,F)XB(F)-OCF3 (2-4-1) 9% 5-HB(F)B(F,F)XB(F,F)-F (2-7-1) 8%5-HHB(F)B(F,F)XB(F,F)-F (2-9-2) 3% 2-HH-3 (3-1-1) 20% V-HH-3 (3-1-1) 28%3-HB-O2 (3-2-1) 4% V2-BB-1 (3-3-1) 5% V-HHB-1 (3-5-1) 5% 1V-HBB-2(3-6-1) 5% 2-BB(F)B-3 (3-7-1) 7% 3-HHB-CL (4-4-1) 6%

0.6 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=79.6° C.; Tc≦−20° C.; Δn=0.100; Δε=2.7; Vth=2.78V; η=13.1 mPa·s;γ1=54.4 mPa·s; τ=8.7 ms; VHR-1-99.0%; VHR-2-98.6%; P=37.6 μm.

Example 12

3-HBBXB(F,F)-F (2-5-1) 7% 5-dhB(F)B(F,F)XB(F)B(F,F)-F (2-16-1) 3%5-GB(F)B(F,F)XB(F)B(F,F)-F (2-17-1) 3% V-HH-3 (3-1-1) 44% 1V-HH-3(3-1-1) 10% V2-BB-1 (3-3-1) 6% 3-HHB-1 (3-5-1) 3% V-HHB-1 (3-5-1) 6%1-BB(F)B-2V (3-7-1) 3% 2-BB(F)B-2V (3-7-1) 3% 5-HGB(F,F)-F (4-14-1) 6%3-GHB(F,F)-F (4-15-1) 6%

0.7 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=79.8° C.; Tc≦−20° C.; Δn=0.093; Δε=3.4; Vth=2.63 V; η=13.5 mPa·s;γ1=54.8 mPa·s; γ=9.1 ms; VHR-1=99.1%; VHR-2=98.5%; P=32.6 μm.

Example 13

3-HHBB(F,F)XB(F,F)-F (2-9-1) 3% 5-BB(F)B(F)B(F,F)XB(F,F)-F (2-11-2) 3%V-HH-3 (3-1-1) 30% V-HH-5 (3-1-1) 7% 7-HB-1 (3-2-1) 4% V2-BB-1 (3-3-1)6% V-HHB-1 (3-5-1) 14% 3-HBB-2 (3-6-1) 3% 1V2-BB-F (4-2) 4% 1V2-BB-CL(4-3) 4% 3-HHB(F,F)-F (4-5-1) 7% 3-BB(F)B(F,F)-F (4-8-1) 9%3-HHB(F)B(F,F)-F (4-11-1) 6%

0.5 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=74.1° C.; Tc≦−20° C.; Δn=0.106; Δε=3.3; Vth=2.65V; η=12.8 mPa·s;γ1=53.1 mPa·s; τ=8.8 ms; VHR-1=99.1%; VHR-2=98.6%; P=41.1 μm.

Example 14

3-BB(F,F)XB(F,F)-F (2-3-1) 6% 3-HBBXB(F,F)-F (2-5-1) 6% 4-HBBXB(F,F)-F(2-5-1) 5% 5-HBBXB(F,F)-F (2-5-1) 7% 3-BB(F)B(F,F)XB(F,F)-F (2-8-1) 3%4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 8% 5-BB(F)B(F,F)XB(F,F)-F (2-8-1) 8%V-HH-3 (3-1-1) 44% V2-BB-1 (3-3-1) 7% V-HHB-1 (3-5-1) 3% 1-BB(F)B-2V(3-7-1) 3%

One part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=77.1° C.; Tc≦−20° C.; Δn=0.118; Δε=5.8; Vth=1.53 V; η=13.2 mPa·s;γ1=55.0 mPa·s; τ=10.8 ms; VHR-1=99.2%; VHR-2=98.8%; P=20.0 μm.

Example 15

5-HXB(F,F)-F (2-1-1) 5% 3-HHXB(F,F)-F (2-2-1) 8% 5-HBBB(F,F)XB(F,F)-F(2-10-1) 3% 5-BB(F)B(F,F)XB(F)B(F,F)-F (2-13-1) 3% V-HH-3 (3-1-1) 26%V-HH-5 (3-1-1) 8% 1V-HH-3 (3-1-1) 5% 3-HH-O1 (3-1-1) 5% 1V2-BB-1 (3-3-1)4% 3-HHEH-5 (3-4-1) 3% VFF-HHB-1 (3-5) 3% 3-HHB-O1 (3-5-1) 3% 3-HB-CL(4-1-1) 9% 3-HBB(F,F)-F (4-7-1) 8% 3-BB(F)B(F,F)-F (4-8-1) 7%

0.8 Part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=75.2° C.; Tc≦−20° C.; Δn=0.095; Δε=3.6; Vth=2.58 V; η=12.4 mPa·s;γ1=51.6 mPa·s; τ=8.1 ms; VHR-1=99.2%; VHR-2=98.7%; P=28.4 μm.

Example 16

3-BB(F,F)XB(F,F)-F (2-3-1) 13% 4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 5%5-HHBB(F,F)XB(F,F)-F (2-9-1) 3% V-HH-3 (3-1-1) 45% 1V-HH-3 (3-1-1) 10%1-BB(F)B-2V (3-7-1) 6% 2-BB(F)B-2V (3-7-1) 7% 3-BB(F)B-2V (3-7-1) 11%

One part by weight of the following compound (1-1-1) was added to 100parts by weight of the composition described above.

NI=73.1° C.; Tc<=−20° C.; Δn=0.121; Δε=3.8; Vth=2.42 V; η=10.6 mPa·s;γ1=47.6 mPa·s; τ=7.7 ms; VHR-1=98.7%; VHR-2=98.5%; P=21.1 μm.

Example 17

3-BB(F,F)XB(F,F)-F (2-3-1) 9% 3-BB(F,F)XB(F)-OCF3 (2-4-1) 8%5-HBB(F,F)XB(F,F)-F (2-6-1) 3% 4-BB(F)B(F,F)XB(F,F)-F (2-8-1) 5%5-HB(F)B(F,F)XB(F)B(F,F)-F (2-12-1) 3% V-HH-3 (3-1-1) 45% 1V-HH-3(3-1-1) 9% V2-BB-1 (3-3-1) 5% V2-BB(F)B-1 (3-7-1) 10% 1O1-HBBH-5 (—) 3%

2 Parts by weight of the following compound (1) was added to 100 partsby weight of the composition described above.

NI=77.1° C.; Tc≦−20° C.; Δn=0.099; Δε=4.9; Vth=1.85 V; η=13.8 mPa·s;γ1=59.4 mPa·s; τ=9.9 ms; VHR-1=99.0%; VHR-2=98.2%; P=50.3 μm.

The compositions in Examples 1 to 17 had a short response time incomparison with those in Comparative Examples 1 and 2. Thus, the liquidcrystal composition of the invention was so much superior incharacteristics to that described in Comparative Examples 1 and 2.

Invention provides the liquid crystal composition that satisfies atleast one characteristic among the characteristics such as a highmaximum temperature of a nematic phase, a low minimum temperature of anematic phase, a small viscosity, a large optical anisotropy, a largedielectric anisotropy, a large specific resistance, a high stability toultraviolet light and a high stability to heat, or that is suitablybalanced regarding at least two of the characteristics. Since a liquidcrystal display device that contains this composition has a shortresponse time, a large voltage holding ratio, a large contrast ratio, along life time or the like, it is suitable for an AM device or the like.

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the disclosure has beenmade only by way of example, and that numerous changes in the conditionsand order of steps can be resorted to by those skilled in the artwithout departing from the spirit and scope of the invention.

1. A liquid crystal composition having a nematic phase that comprisestwo components, wherein the first component is at least one opticallyactive compound selected from the group of compounds represented byformula (1), and the second component is at least one compound selectedfrom the group of compounds represented by formula (2):

wherein R¹ and R⁴ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine; R² and R³ are each different and are alkyl having 1 to 12carbons or alkenyl having 2 to 12 carbons; ring A, ring B and ring C areeach independently 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,3,5-difluoro-1,4-phenylene or 2,5-pyrimidine; Z¹ and Z² are eachindependently a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy; X¹ and X² are each independently hydrogen orfluorine; Y¹ is fluorine, chlorine or trifluoromethoxy; and k and m areeach independently 0, 1, 2 or 3, and the sum of k and m is 3 or less. 2.The liquid crystal composition according to claim 1, wherein the sum ofthe number of carbons in R² and R³ of formula (1) is in the range of 3to
 10. 3. The liquid crystal composition according to claim 1, whereinthe first component is at least one compound selected from the group ofcompounds represented by formula (1-1):

wherein R¹ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine.
 4. Theliquid crystal composition according to claim 1, wherein the secondcomponent further comprises at least one compound selected from thegroup of compounds represented by formula (2-1) to formula (2-13):

wherein R⁴ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine; X¹, X², X³,X⁴, X⁵, X⁶, X⁷, X⁸ and X⁹ are each independently hydrogen or fluorine;and Y¹ is fluorine, chlorine or trifluoromethoxy.
 5. The liquid crystalcomposition according to claim 4, wherein the second component, is atleast one compound selected from the group of compounds represented byformula (2-3).
 6. The liquid crystal composition according to claim 4,wherein the second component is at least one compound selected from thegroup of compounds represented by formula (2-8).
 7. The liquid crystalcomposition according to claim 1, wherein the ratio of the firstcomponent is in the range of approximately 0.01 part to approximately 5parts by weight based on 100 parts by weight of the liquid crystalcomposition excluding the first component.
 8. The liquid crystalcomposition according to claim 1, wherein the ratio of the secondcomponent is in the range of approximately 5% to approximately 55% byweight based on the weight of the liquid crystal composition excludingthe first component.
 9. The liquid crystal composition according toclaim 1, wherein the composition further comprises at least one compoundselected from the group of compounds represented by formula (3) as athird component:

wherein R⁵ and R⁵ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine; ring D and ring E are each independently 1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene or2,5-difluoro-1,4-phenylene; Z³ is independently a single bond, ethyleneor carbonyloxy; and p is 1 or
 2. 10. The liquid crystal compositionaccording to claim 9, wherein the third component is at least onecompound selected from the group of compounds represented by formula(3-1) to formula (3-7):

wherein R⁵ and R⁶ are each independently alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons, alkenyl having 2 to 12 carbons, oralkenyl having 2 to 12 carbons in which arbitrary hydrogen is replacedby fluorine.
 11. The liquid crystal composition according to claim 10,wherein the third component is a mixture of at least one compoundselected from the group of compounds represented by formula (3-1), atleast one compound selected from the group of compounds represented byformula (3-5), and at least one compound selected from the group ofcompounds represented by formula (3-7).
 12. The liquid crystalcomposition according to claim 9, wherein the ratio of the thirdcomponent is in the range of approximately 35% to approximately 95% byweight based on the weight of the liquid crystal composition excludingthe first component.
 13. The liquid crystal composition according toclaim 1, wherein the composition further comprises at least one compoundselected from the group of compounds represented by formula (4) as afourth component:

wherein R⁷ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine; ring F isindependently 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, 1,4-phenylene,2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,3,5-difluoro-1,4-phenylene or 2,5-pyrimidine; Z⁴ is independently asingle bond, ethylene or carbonyloxy; X¹⁰ and X¹¹ are each independentlyhydrogen or fluorine; Y² is fluorine, chlorine or trifluoromethoxy; andq is 1, 2 or
 3. 14. The liquid crystal composition according to claim13, wherein the fourth component is at least one compound selected fromthe group of compounds represented by formula (4-1) to formula (4-11):

wherein R⁷ is alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, or alkenyl having 2 to 12carbons in which arbitrary hydrogen is replaced by fluorine.
 15. Theliquid crystal composition according to claim 14, wherein the fourthcomponent is a mixture of at least one compound selected from the groupof the compounds represented by formula (4-5) and at least one compoundselected from the group of compounds represented by formula (4-8). 16.The liquid crystal composition according to claim 14, wherein the fourthcomponent is a mixture of at least one compound selected from the groupof the compounds represented by formula (4-7) and at least one compoundselected from the group of compounds represented by formula (4-8). 17.The liquid crystal composition according to claim 13, wherein the ratioof the fourth component is in the range of approximately 3% toapproximately 45% by weight based on the weight of the liquid crystalcomposition excluding the first component.
 18. The liquid crystalcomposition according to claim 1, wherein the maximum temperature of anematic phase is approximately 70° C. or higher, the optical anisotropy(25° C.) at a wavelength of 589 nm is approximately 0.08 or more, andthe dielectric anisotropy (25° C.) at a frequency of 1 kHz isapproximately 2 or more.
 19. A liquid crystal display device comprisingthe liquid crystal composition according to claim
 1. 20. The liquidcrystal display device according to claim 19, wherein an operating modeof the liquid crystal display device is a TN mode, an OCB mode, an IPSmode or a PSA mode, and a driving mode of the liquid crystal displaydevice is an active matrix mode.